This invention relates to the field of acoustic devices, and more particularly to bending wave loudspeakers, also known as distributed mode loudspeakers (DMLs), including acoustic radiators and transducers.
Cellular phones, televisions, and like products often include loudspeakers having a diaphragm excited by an axially driven transducer. Such speakers are relatively large for products where space is at a premium and where there is a continual drive to reduce the size of the products. In a recently developed alternative to conventional piston-driven loudspeakers, sound may be produced by bending wave loudspeakers. Bending wave loudspeakers may use the device's display as an acoustic radiator, recognizing space savings by eliminating a relatively large conventional speaker. Further, in some cases the listening experience produced by a bending wave loudspeaker is superior to that of a conventional speaker in that the sound coming from a DML is not as localized as that produced by traditional receivers.
Bending wave loudspeakers include an acoustic radiator that is capable of supporting bending wave vibration and an electromechanical transducer mounted to the acoustic radiator. Bending wave energy may be transmitted to the acoustic radiator by a transducer, or exciter, to generate bending waves in the radiator, which may be a panel, and produce an acoustic output. The exciter is mounted to the panel, and may be a dynamic exciter such as an electromechanical moving coil or other inertial exciter, a piezoelectric exciter, or the like. A piezoelectric exciter is often preferable as compared to other types of exciters because it is generally smaller (and in particular thinner) and lighter. Piezoelectric materials, however, are also relatively brittle and fragile. Electronic acoustic devices, and particularly handheld ones, are susceptible to being dropped or otherwise jarred, and the piezoelectric material, rigidly mounted to the acoustic radiator, is subjected to impact force and possible breakage.